A “sick house” is one where the building itself is causing health problems: headaches, fatigue, throat irritation, dry coughs, itchy skin, difficulty concentrating, or worsening allergies and asthma. These symptoms appear when you’re home and improve when you leave. The cause is almost always some combination of poor ventilation, moisture problems, chemical fumes from household products, or biological contaminants like mold. Curing a sick house means identifying which of these factors is at play and systematically eliminating them.
Recognize the Symptoms
Sick building syndrome was originally studied in offices, but the same dynamics apply to homes. The hallmark is that symptoms are tied to time spent inside. You might notice eye, nose, or throat irritation, dizziness, nausea, dry skin, a hoarse voice, or flu-like symptoms that clear up after a few hours away from home. Some people develop sensitivity to odors or experience personality changes like increased irritability. If multiple household members are affected, or if symptoms cluster in one room, the building is almost certainly the problem.
Find the Source
Before you start fixing anything, you need to figure out what’s contaminating your air. The four main culprits are moisture and mold, chemical off-gassing, outdoor pollutants entering the home, and inadequate ventilation.
A DIY indoor air quality monitor is a reasonable starting point. Consumer-grade devices can track humidity, particulate matter, and basic volatile organic compounds (VOCs). They’re useful for routine monitoring and can flag obvious problems. But they can’t match the precision of professional testing, which uses laboratory analysis, infrared cameras, and certified experts to detect the full spectrum of contaminants: mold spores, formaldehyde, carbon monoxide, radon, and other hazardous chemicals. If you’ve recently moved in, had water damage, or experienced a fire, professional testing is worth the investment. It’s also the only option that produces documentation valid for insurance claims or real estate disputes.
Start with a visual and sensory inspection. Look for water stains on ceilings and walls, condensation on windows, musty smells in basements or bathrooms, and visible mold. Check under sinks, behind appliances, and around HVAC vents. Note whether symptoms worsen after cooking, cleaning, or when certain systems run.
Fix Moisture and Remove Mold
Mold is one of the most common drivers of a sick house. It breeds wherever moisture lingers: leaky pipes, poor drainage, condensation on cold surfaces, wet carpet, and damp ceiling tiles. The EPA’s guidance is clear: if mold is present, you must fix the water source first. Cleaning mold without solving the moisture problem guarantees it will return.
Act fast when water intrusion happens. Water-damaged materials need to be dried within 24 to 48 hours to prevent mold growth. On hard surfaces, scrub mold off with detergent and water, then dry completely. Porous materials like carpet, ceiling tiles, and upholstered furniture often can’t be salvaged and should be discarded. Never paint or caulk over a moldy surface.
A few important precautions during cleanup: wear an N-95 respirator, long gloves, and non-vented goggles. Bleach is not recommended as a routine mold cleaner, and you should never mix bleach with ammonia-based products, which creates toxic fumes. If your HVAC system is contaminated, don’t run it during cleanup or it will spread spores throughout the house. Dead mold still triggers allergic reactions, so killing it isn’t enough. It has to be physically removed.
Keep indoor humidity between 30 and 50 percent relative humidity. Anything above 60 percent creates conditions for condensation and mold growth. A basic hygrometer costs under $20 and tells you exactly where you stand. Use dehumidifiers in basements and bathrooms, vent dryers to the outside, and run exhaust fans when showering or cooking.
Reduce Chemical Contaminants
Volatile organic compounds are invisible gases released by an enormous range of household products: paints, varnishes, cleaning sprays, disinfectants, scented candles, air fresheners, aerosol sprays, new furniture, carpeting, and pressed wood products. Gasoline and other chemicals stored in an attached garage also migrate into living spaces. These compounds cause headaches, respiratory irritation, and fatigue, sometimes at concentrations you can’t even smell.
The most effective strategy is source elimination. Switch to low-VOC or no-VOC paints and finishes. Replace aerosol cleaning products with pump bottles or simple alternatives like vinegar and baking soda. Store fuels, solvents, and paints in a detached garage or shed, tightly sealed. Dispose of old chemicals you no longer need.
New furniture, carpets, and mattresses off-gas most heavily in the first days and weeks, but carpets can continue releasing VOCs for five years or more. Some materials never fully stop. Ventilation is the only proven mitigation short of removing the item entirely. When new carpet is installed, open windows and run fans blowing air outdoors for at least 72 hours, and ideally for several weeks afterward. If possible, ask the supplier to unroll and air out carpet in their warehouse before delivery. For new furniture, unwrap it and let it off-gas in a well-ventilated space for several days before bringing it into your bedroom or living area.
Improve Ventilation
Inadequate ventilation is a root cause of nearly every sick house problem. Tight construction, sealed windows, and poorly maintained HVAC systems trap pollutants inside. The current standard for residential buildings recommends at least 0.35 air changes per hour, meaning roughly a third of your home’s air volume should be replaced with fresh outdoor air every hour, with a minimum of 15 cubic feet per minute per person.
In practical terms, this means opening windows regularly, especially when cooking, cleaning, or using products that emit fumes. Run kitchen and bathroom exhaust fans that vent to the outside (not into the attic). If your home is tightly sealed for energy efficiency, consider a mechanical ventilation system like a heat recovery ventilator (HRV) or energy recovery ventilator (ERV), which brings in fresh air without losing all your heating or cooling.
Check that your HVAC air intake vents aren’t located near sources of outdoor pollution like driveways, dumpsters, or exhaust outlets from other parts of the building. Combustion byproducts from a nearby or attached garage can enter through poorly placed vents and openings.
Upgrade Your Air Filtration
Your HVAC filter is your home’s first line of defense against airborne particles. Filters are rated on the MERV scale, where higher numbers mean better particle capture. Most basic residential filters are rated MERV 1 to 4, which catch less than 20 percent of even the largest particles. That’s essentially doing nothing for your health.
The EPA recommends upgrading to at least a MERV 13 filter, or the highest rating your system can handle. A MERV 13 filter captures 50 percent or more of the finest particles (0.3 to 1.0 microns, which includes bacteria and some smoke particles) and 85 to 90 percent of mid-range particles like mold spores and dust mite debris. For comparison, a true HEPA filter captures 99.97 percent of particles at 0.3 microns, but most residential HVAC systems can’t accommodate one without modification.
Before upgrading, check your system’s specifications. A filter that’s too restrictive for your blower motor will reduce airflow, strain the system, and potentially make things worse. If your HVAC can’t support a high-MERV filter, a standalone portable air purifier with a HEPA filter in key rooms is a solid alternative. Change filters on the manufacturer’s recommended schedule, and more often if you have pets or live in an area with high outdoor pollution.
Test for Radon
Radon is a radioactive gas that seeps into homes from the ground. You can’t see, smell, or taste it, and it’s the second leading cause of lung cancer. The EPA recommends fixing your home if radon levels reach 4 pCi/L (picocuries per liter) or higher. Because there is no known safe level of radon exposure, they also recommend considering mitigation for levels between 2 and 4 pCi/L.
Testing is simple. Hardware stores sell short-term test kits for under $20, or you can order one from your state radon office (often free). Place the kit in the lowest livable level of your home for the recommended period, then mail it to a lab. If your results are elevated, a radon mitigation system, which typically involves a vent pipe and fan that pulls radon from beneath the foundation and exhausts it above the roofline, can reduce levels by up to 99 percent.
What About Houseplants?
The idea that houseplants purify indoor air traces back to a well-known NASA study, but the reality is more complicated. Those experiments were conducted in sealed chambers, not real homes with constant air exchange. Researchers at the University of Georgia have noted that the number and type of plants needed for meaningful air purification would have to be tailored to each building, and that it’s not yet possible to project the true potential of plants for cleaning indoor air. The effect, while generally positive, is too small to replace ventilation, source control, or filtration. Enjoy your plants for other reasons, but don’t rely on them to cure a sick house.
A Room-by-Room Approach
Curing a sick house works best when you treat it as a series of targeted problems rather than one vague air quality issue. In the kitchen, make sure your range hood vents outdoors and that you use it every time you cook with gas. In bathrooms, run exhaust fans during and for 15 to 20 minutes after showers. In bedrooms, focus on dust mite control through humidity management, washable bedding, and air filtration. In the basement, address water intrusion, dehumidify, and test for radon. In the garage, never idle a car inside, seal the door to the living space, and move chemical storage to a detached structure if possible.
The core principle is the same in every room: control moisture, eliminate chemical sources, and move fresh air through the space. Most sick houses aren’t caused by a single dramatic problem. They’re the result of several minor issues compounding in a sealed environment. Address them one by one and your symptoms will typically improve within days to weeks, depending on the severity of the contamination.